A unidirectional DC-DC converter which converts a supplied voltage into a desired voltage can increase the conversion efficiency by reducing switching losses by soft switching technology. Simultaneously, it is possible to downsize inductors, capacitors, and other passive elements by increasing driving frequencies of switching elements.
Japanese Patent Laid-open No. 2005-318766 (Patent Document 1) discloses a unidirectional DC-DC converter which can perform soft switching. In the main circuit of the DC-DC converter, main switching element is directly connected to a DC power supply. An inductor and a load are connected in series thereto. An auxiliary resonance circuit including an auxiliary switching element is connected to a series circuit of the DC power supply and the main switching element.
Further, Turuta et al, “Proposal and experiments of 98.5% High Efficiency Chopper Circuit QRAS for electric vehicles” Institute of Electrical Engineers Article D 2005, Vol. 125 No. 11 (Non-Patent Document 1) discloses a unidirectional DC-DC converter of a zero-current switching (ZCS) type which suppresses the rate-of-change of current of the main switching element.
Japanese Patent Laid-open No. 2004-129393 (Patent Document 2), for example, discloses a circuit configuration of a bidirectional DC-DC converter which can perform soft-switching.